Question

我试图从我的数据库中的表中清除所有数据，它是成功的，但唯一的问题是，每次我按下清除按钮，它确实清除所有数据但是之后应用程序显示它已经停止

我哪个部分出了问题？以下是我的数据库编码：

public boolean deleteRow(long id) {

        SQLiteDatabase db = helper.getWritableDatabase();
        String where = data.UID + "=" + id;
        return db.delete(data.TABLE_NAME, where, null) != 0;
    }

    public void DeleteAll(){

        Cursor c = readEntry();
        long id = c.getColumnIndexOrThrow(data.UID);
        if (c.moveToFirst()) {
            do {
                deleteRow(c.getLong((int) id));
            } while (c.moveToNext());
        }
        c.close();
        return;
    }

和来自其他java的代码：

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.showbmi);
        initializeApp();
    }
    private void initializeApp(){

        weightinputid = (EditText) findViewById(R.id.weightid);
        heightinputid = (EditText) findViewById(R.id.heightid);
        buttonBMI = (Button) findViewById(R.id.buttonBMI);
        BMIfinal= (TextView) findViewById(R.id.BMIfinal);
        BMIStatus = (TextView) findViewById(R.id.BMIstatus);
        save = (Button) findViewById(R.id.button);
        detail = (Button)findViewById(R.id.button1);
        bb = (Button)findViewById(R.id.bb);
        table_layout = (TableLayout) findViewById(R.id.tableLayout1);

        data  = new fitnessdatabase(this);
        BuildTable();
        bb.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                data.DeleteAll();
                new MyAsync().execute();
            }
        });



private class MyAsync extends AsyncTask<Void, Void, Void> {

        @Override
        protected void onPreExecute() {

            super.onPreExecute();

            table_layout.removeAllViews();

            PD = new ProgressDialog(Showbmi.this);
            PD.setTitle("Please Wait..");
            PD.setMessage("Loading...");
            PD.setCancelable(false);
            PD.show();
        }

        @Override
        protected Void doInBackground(Void... params) {

            String weight = weightinputid.getText().toString();
            String bmi = BMIfinal.getText().toString();
            String status = BMIStatus.getText().toString();
            String date1 = mDateText.getText().toString();

            // inserting data
            data.open();
        //    sqlcon.insertData(firstname, lastname);
            long id = data.insertData(weight, bmi, status, date1);
            BuildTable();
            return null;
        }

        }

来自logcat的错误如下所示：

java.util.concurrent.FutureTask.setException(FutureTask.java:219)
            at java.util.concurrent.FutureTask.run(FutureTask.java:239)
            at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
            at java.lang.Thread.run(Thread.java:856)
     Caused by: java.lang.NullPointerException
            at com.example.adiehabs.fitnessku.Showbmi$MyAsync.doInBackground(Showbmi.java:188)
            at com.example.adiehabs.fitnessku.Showbmi$MyAsync.doInBackground(Showbmi.java:169)
            at android.os.AsyncTask$2.call(AsyncTask.java:287)
            at java.util.concurrent.FutureTask.run(FutureTask.java:234)

Answer 1

当您尝试data.Open()时，它会触及一个未初始化的变量，因为您已经在私人虚空中进行了初始化。将其更改为公开或将所有代码放入您创建的包中。由于UI控件也将为null。

编辑您使用logcat更新后确认了这一点。在背景中做。

引起：java.lang.NullPointerException 在com.example.adiehabs.fitnessku.Showbmi $ MyAsync.doInBackground（Showbmi.java:188）

private void initializeApp(){

if (c.moveToFirst()) {
        do {
            deleteRow(c.getLong((int) id));
        } while (c.moveToNext());
    }

我会用：将光标移动到第一个，只有在它没有经过最后一个项目时才移动它。

  c.moveToFirst(); 
       while(!c.isAfterLast()) {
            deleteRow(c.getLong((int) id));
           c.moveToNext();
        } 
    }

另一件事：

您是否已在主范围table_layout，PD中声明了这些变量？应用程序没有响应通常来自nullpointer异常。

Answer 2

删除所有表格行

public boolean deleteTable(){

    return mSQLiteDatabase.delete(DataBaseHelper.TABLE, null, null) > 0;
}

当我试图清除所有数据时，应用程序已停止

2 个答案: